Sensory ganglia contain two populations of neurons which can be identified by their size, organelle content, degree of myelination, or histochemical profile. Since the chemical capsaicin (the hot ingredient of red peppers) is neurotoxic to one of the groups of sensory neurons when injected into newborn rats, we used this drug to determine which type of neuron is responsible for causing taste bud development. Capsaicin treatment destroyed many of the B-type sensory neurons, but this loss did not interfere with the temporal pattern of development, number, or degree of innervation of the buds. It can therefore be concluded that the A-type sensory cells are the gustotrophic neurons. In another study, denervated tongue tissue was reinnervated by hypoglossal motor fibers in order to help resolve why these axons cannot induce taste buds. Although regenerated motor fibers were observed in the connective tissue of the tongue, none of these axons penetrated the epithelium where the buds are normally found. Since the axons must enter the epithelium to induce buds, this result suggests that certain sensory but not motor axons are endowed with some unique property which permits them to enter and remain within appropriate epithelium.